THE SNP hailed an "exceptional" Scottish Parliament by-election victory by holding on to Aberdeen Donside with a reduced majority.

Winning in the city reflects well on the party approaching half way through its second term of government at Holyrood, Deputy First Minister Nicola Sturgeon said.

SNP candidate Mark McDonald kept the seat with almost 42% of the vote.

But the share fell by 13% compared with the 2011 national election, which was won by the SNP's Brian Adam, who died in April.

Labour saw its share increase by almost 5%, leading to claims the seat is there for the taking at the next Holyrood election in 2016.

Ms Sturgeon, speaking the morning after the poll, said: "For a government that is mid-term into our second term of government, this was an exceptional result and a fantastic victory.

"People responded positively to the SNP's record in government, our billion pounds of investment in Aberdeen's infrastructure, and of course Brian Adam's legacy."

She dismissed Labour's challenge as a "powderpuff performance" and said: "The swing to Labour was just 9% - a very poor result after six years in opposition."

Mr McDonald, who stood down as a regional North East MSP to fight the contest, marked his first day as a constituency member with a pledge to challenge local council proposals to close two schools.

"The people of Donside have spoken and Aberdeen City Council must listen," he said.

He won the seat with 9,814 votes compared with 7,789 for Labour candidate Willie Young, who was the closest rival.

The Liberal Democrats took third place with 1,940 votes, leapfrogging the Conservatives who took 1,791 votes.

Ukip, which has no elected representation in Scotland, won 1,128 votes and lost its deposit.

First Minister Alex Salmond, the SNP leader, congratulated his candidate shortly after the victory was declared in the early hours.

"This is a very bad result for Labour," he said.

"After six years of opposition, they show no sign of being anything more than an opposition party.

"I am also delighted that Ukip failed to retain their deposit. They have never saved a single deposit in Scotland, which once again demonstrates a clear divergence between Scottish and Westminster politics."